1640s, "to shake or disturb by violent, irregular action" (transitive); 1680s, "to draw or contract spasmodically or involuntarily" (intransitive); from Latin convulsus, past participle of convellere (transitive only) "to pull away, to pull this way and that, wrench," hence "to weaken, overthrow, destroy," from assimilated form of com "with, together" (see con-) + vellere "to pluck, pull violently" (see svelte). Related: Convulsed (1630s); convulsing.
